The Odds are Good, but the Goods are Odd

Sports fans are constantly bombarded with data and information, even in a simple and straightforward sport like MMA. As any sport grows, the metrics that measure it and the statistics that report it evolve. However, there’s one set of numbers that are omnipresent from the start of almost any sport: the betting odds.

In MMA, the Tale of the Tape summarizes the basic physique of the fighters, while their record summarizes their performance history. It’s the betting line, however, that is the most direct and immediate hint to what’s about to happen when the cage door shuts. Let’s
take a closer look at what the odds can tell us about MMA, matchmaking, and upsets.

Only a small portion of fights are evenly matched according to oddsmakers. “Pick ‘Em” fights make up only 12% of all matchups in the UFC, with the rest of the fights having a clear favorite and underdog. Dana White mentions these betting lines to help build the story around matchups, often to point out why a particular fighter might be a “live dog.”

In an academic sense, betting lines are basically the market price for a certain event or outcome. These prices can move accordingto betting activity leading up to the event. When a UFC fight begins, the betting line is the public’s final perception of the probability of each fighter winning, with roughly half of people betting on each side of the line. Many experts make bold and confident predictions about fights, and they’re wrong a good portion of the time. But what about the odds? How do we tell if they’re right?

WHAT DO ODDSMAKERS KNOW?

In a macro sense, cage fighting is inherently difficult to predict for a variety of reasons. The young sport is competed by individuals, and there are no teammates in the cage to help pick up the slack or remedy mistakes. Individual competitors only fight for mere minutes per outing, and if they’re lucky, only a few times per year. And let’s not forget the raw and primal forces at work in the cage. The volatility of these factors mean there is absolutely no such thing as a guaranteed win when you’re allowing one trained competitor unmitigated access to do violence on another. The action is completely dynamic—and often intense—with only a few round breaks to reset the match. These are reasons we watch and love the sport—it’s fast, furious, and anything can happen. It’s the polar opposite of the true statistician’s sport: baseball.

Given how difficult MMA might be to predict and quantify compared to other mainstream team sports, it could be very revealing to look at how accurate oddsmakers have been over the last few years of UFC events. For this analysis, I’ve translated the odds from the standard American odds format. For example, a -200 line indicates a 2:1 favorite, while +300 is a 3:1 underdog. We can convert these somewhat confusing numbers to a percentage that is the implied win probability based on the odds at fight time (or 67% and 25% for these examples, respectively). If 10 fighters were listed as slight underdogs with a 40% implied win probability, we should expect four of them to win and six to lose, if the odds were accurately set.

It turns out that oddsmakers have been pretty good at assessing the likelihood of fight outcomes. There odds-based predictions closely match the actual outcomes of the fights. The exception to this occurs at the extreme end of the spectrum, where very heavy underdogs have been over-performing by winning more fights than expected over heavy favorites. The sample size for this group is the smallest one of all, so don’t go betting your life on long shots just yet.

We also see a slight drop in the middle of the betting spread. Slight favorites could be losing at a higher than predicted rate due to some basic bias of the betting public. When two guys fight who appear to be very evenly matched, most bettors pick the more famous name. This is one possible explanation for favorites under performing against the implied win probability of the betting lines.

PATTERNS IN THE CHAOS

The betting line allows us to view fights through the lens of how evenly matched the fighters are. In theory, if betting lines are accurate, more extreme spreads mean the fighters are mismatched against each other. Conversely, when two fighters are very evenly matched, it’s rare to see one dominate the other. What does the evenness of the matchup mean for how fights play out?

One clear pattern that emerges is when there is a significant mismatch between fighters. When fighters are mismatched, finish rates go up. This makes sense, because either the favorite truly is much better than their opponent, and hence more likely to finish them, or the underdog pulls off a miraculous move that finishes the fight.

We’ve already seen that betting lines are generally accurate. At face value, there’s no particular betting line where outcomes are drastically different from the expectation set by the odds. But we also know, generally speaking, almost a third of fights will not end as the masses predicted. Heavier fighters tend to have slightly higher upset rates, perhaps because the “puncher’s chance” means more when larger fighters land that one fight-ending strike. There are also almost twice as many upsets in co-main events than in main events. Either way, there are no guaranteed outcomes in MMA, and there is the potential for a spectacular finish in every fight. That’s what makes MMA an exciting sport. If you don’t believe that, here are 10 reminders.

WHAT DID WE LEARN?

Betting lines are generally an accurate predictor of who will win a fight.

30% of the fights with a clear favorite/underdog result in an upset.

Only 12% of UFC fights are an even “Pick ‘Em.”

The more extreme the betting line, the more likely there will be a finish.

Co-main events see the highest rate of upsets at 40%—main events the lowest at 23%.